1. Technical Field
The present invention relates to an ink composition, an ink set, and an image forming method.
2. Related Art
An inkjet recording method is a method of performing recording by ejecting ink in the form of liquid droplets from a number of nozzles provided in an inkjet head. The inkjet recording method is widely used since high quality images can be recorded on various recording media by the method.
In black inks for inkjet recording, carbon black pigment is used. On the other hand, for color inks, water-soluble dyes are mainly used and improvement in weather resistance (for example, light-fastness, ozone resistance and water resistance) of the water-soluble dyes is desired. Considering application of the water-soluble dyes to the field of printing, improvement in weather resistance is especially important. Pigments, having a high crystallinity, are superior to dyes especially in light fastness and water resistance. However, there are still problems to be addressed in that storage stability of pigment inks is insufficient, and that rubbing resistance of a printed matter may decrease due to pigment particles remaining on the surface of a recording medium.
As a technique for improving rubbing resistance of a recorded image, an ink composition which contains water, a pigment covered with a water-insoluble polymer, and at least two kinds of wax having different average particle diameters, is disclosed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2007-277290).
Further, as a technique for improving rubbing resistance of a recorded matter, an ink composition which contains an alkali-soluble copolymer, water, a colorant and a wax, the alkali-soluble copolymer having a pH being adjusted so that the alkali-soluble copolymer is water-soluble by inorganic base and having an acid value of 40 or less, is disclosed (for example, see JP-A No. 2003-261805).
However, although the ink composition of JP-A No. 2007-277290 may improve rubbing resistance of a recorded image as a result of adding two kinds of waxes having different average particle diameters, the obtained recorded image is yet to be improved in terms of blocking resistance immediately after the printing.
Moreover, although the ink composition of JP-A No. 2003-261805 may improve rubbing resistance of recording paper for inkjet recording, there is room to be improved in rubbing resistance of other recording media such as plain paper.
The present invention is made in view of the aforementioned background, and one object of the present invention is to provide an ink composition which is capable of forming an image having excellent temporal storage stability and having excellent blocking resistance immediately after the printing; an ink set employing the ink composition; and an image forming method using the ink composition.